Using data from the 24,000 tumors (550,000 patient-years-at-risk) reported at the Veterinary Medical Data Program through December 1973, we expect to provide a reference of the distribution of spontaneous tumors in domestic animals. Further, using this relatively large series, we intend to search for unusual zoographic distributions of tumors, which may suggest possible clues regarding the etiology of cancer. The patient characteristics we expect to emphasize are age, breed/species, sex; the tumor characteristics are degree of malignancy, site and histogenic type. Only the bovine, equine, feline and canine species had a sufficient number of tumors reported to be of value in analytic studies. Currently conducting studies on intranasal tumors, multiple primary tumors, prostatic tumors, mammary tumors.